Engineering topics
Publications and source records attributed to Schmidt, G. D..
Optical broad-band polarimetry is presented for near-infrared color-selected active galactic nuclei (AGN) classified as quasi-stellar objects (QSOs) based on their Ks-band luminosity.
The polarimetric capabilities of Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) are demonstrated from data obtained during the Early Release Observations of IRC+10216 and CRL 2688 (the Egg Nebula). Preflight Thermal Vacuum tests revealed that each polarizer has a unique polarizing efficiency, and that the position angle offsets differ from the nominal positions of O deg, 120 deg and 240 deg. Therefore an algorithm different from that of an ideal polarizer is required for proper reduction of astronomical polarimetry data. We discuss this new algorithm and the results of its application to NICMOS data. We also present preliminary estimates of the Instrumental Polarization, the sensitivity of the grisms to polarized light, and the accuracy of NICMOS imaging polarimetry for faint and low polarization objects. Finally, we suggest strategies for maximizing the success of NICMOS polarimetry observations.
Comparison of the period distributions of various classes of CVs confirms an extreme bias of the synchronous AM Her systems toward short orbital periods, while the DQ Her systems do not differ significantly from the distribution of nonmagnetic systems. This suggests either strong selection effects or enhanced evolution of the AM Her systems. There is as yet no obvious bimodality in either the magnetic field distributions of isolated white dwarfs or of CV primaries. However, clear differences between the two exist: the strongest being that magnetic primaries are overrepresented among short period CVs by more than an order of magnitude in comparison to the field white dwarfs.
A comprehensive analysis of E 1114 + 182, the first eclipsing AM Herculis binary system and the shortest-period eclipsing cataclysmic variable known, is presented. The time-resolved X-ray observations which led to the system's recognition as an AM Her system with a roughly 90 minute orbital period are reported. The current optical photometric and polarimetric ephemeris and a description of the system's phase-modulated properties are given. The detailed photometric eclipse profile and the highly variable spectroscopic behavior are addressed. This information is used to determine systemic parameters and derive new information on the line emission regions. The data put severe constraints on current torque models for keeping the binary and white dwarf rotation in phase.
The discovery of two magnetic white dwarfs culled from blue star surveys is reported. The surveys were carried out with the Mount Lemnon 1.5-meter reflecting telescope attached to a two-holer polarimeter/photometer. Spectral observations of the objects, (PG 1533 - 057, and K813 - 14), indicate the presence of hydrogen and Zeeman components. On the basis of dipolar field simulations, it is shown that PG 1533 - 057 has a polar field strength of 31 megagauss (MG) while K813 - 14 has a polar field strength of 29 MG. A third known white dwarf has a polar field strength of 18 MG. All the dwarfs had temperatures in the 11,000-20,000 K range. The possibility that a significant fraction of isolated magnetic degenerate stars could be the progeny of magnetic accreting binary systems is considered.
In the present optical polarimetry and IR photometry for the broad line radio galaxy 3C 109, the absence of variability, in conjunction with a polarization in H-alpha that is identical to that of the adjacent continuum, suggests that the strong polarization of this galaxy is due to extinction by aligned dust grains. This is the process which gives rise to interstellar polarization within the Galaxy. The energy output of 3C 109, from the optical to 20 microns, exceeds by a factor of 2-4 that of the Seyfert 1 galaxy Markarian 231. These observations, together with recent polarimetry of other broad line radio galaxies, indicate that their broad line regions are more heavily reddened than those of either the Seyfert 1 galaxies or quasars. Evidence for a gradual decrease in dust content with increasing source luminosity is discussed.
The bright soft X-ray source E2003 + 225, originally discovered by the HEAO 1 low-energy detectors, has been found to be a new AM Herculis type binary. The optical counterpart shows a rich emission spectrum of He II, He I, and H as well as circular and linear polarization. Larger polarization in the near-infrared than in the ultraviolet argues for its origin as high harmonic cyclotron emission. Optical photometry, polarimetry, spectroscopy, and the X-ray light curves are all consistent with an orbital period of 222.51 m, the longest period known for AM Herculis systems, and only the second on the long side of the 2-3 hour cataclysmic variable period gap.
Two hot stars discovered in the Palomar Green survey which were found to exhibit peculiarly broad and strong Balmer lines possibly indicative of low magnetic fields are discussed. The stars, PG 1658+441 and PG 0136+251, were found to have extended trough-shaped Balmer and Lyman-alpha line profiles when compared to nonmagnetic dwarfs of similar temperatures. Further observations of PG 1658+441 show it to correspond to a 30,000 K pure hydrogen atmosphere and confirm its nature as a magnetic object with a longitudinal field strength of about 0.7 megagauss and a mean surface field of about 2.3 megagauss. PG 0136+251 is found to be a hotter star (40,000-50,000 K) with weaker lines. Although no strong evidence for magnetic line splitting was obtained, it is argued that neither a high surface gravity nor very rapid rotation can account for the Balmer line shapes. Results thus extend the range of magnetic degenerates to include very hot white dwarfs, and demonstrate the usefulness of line-widths as indicators of possible low-field magnetic sources.
Optical spectropolarimetry of three dust-enshrouded carbon stars reveals very large degrees of polarization, requiring highly organized circumstellar dust shells around each object. The extremely peculiar spectral behavior of polarization for GL 1403 implies two orthogonally polarized spectral components: one due to hot dust; the other, the stellar photosphere. The observations of this object are interpreted in terms of a cool dust torus and bipolar scattering lobes. Such a structure, together with a 635 day photometric period derived from IR observations, supports evolution of high-mass carbon variables into bipolar nebulae.
Spectrophotometric and spectropolarimetric observations are presented of three HH objects: HH 11, 30, and 43. Although null polarization results are obtained for HH 11 and 43, the unusually strong continuum of HH 30 is linearly polarized by 3%. The emission lines in this nebula are unpolarized. The electric vector position angle appropriate to the continuum polarization, and the presence of Fe II emission lines apparently from the photosphere of a T Tauri-like star, indicate HL Tau as the exciting/illuminating star for HH 30. Evidence is adduced for a highly anisotropic distribution of circumstellar obscuration around this star.
Optical spectropolarimetry and spectrophotometry are presented of the two bipolar nebulae GL 618 and M2-9. A comparison of the polarization in the emission lines and the continuum is used to construct geometrical and physical models for each object. It is found that the forbidden lines arise largely in the visible nebulae, whereas the permitted lines are formed in a central high-density region and are scattered with the stellar continuum by dust grains in the lobes. Condensations are found to be an important component of the lobes, reinforcing the view that these bipolars represent a very early phase in the life of a planetary nebula.
A Cassegrain spectrograph used in conjunction with an image-tube, image-dissector scanner (ITS) is discussed with reference to its design features and operation. The spectrograph has a remote control feature, and its parameters, such as slit width, decker position, filter selection, focus, and grating selection, can be easily changed by computer command or a hard-wired control box. The discussion also includes the area scanner modification which allows raster scanning and limited picture taking. Finally, the design of a two-channel polarization analyzer is presented which allows simultaneous sky and sky-plus-star observations and faint-object polarimetry.
Spectrophotometry and spectropolarimetry with HD 44179 are presented. These measurements reveal that the very broad bump evident in previous low-resolution spectra possesses a large amount of structure, including groups of narrow emission lines and several diffuse features. A reduction in polarization, but constant position angle, through the bump indicates that this emission originates within the nebula itself and merely dilutes the polarized scattered starlight. A few very weak atomic emission lines are detected, but the overall feature, which strongly resembles the emission spectra of some molecules, remains unidentified. Constraints on the excitation mechanism are discussed.
Report evaluates ultrasonic bonding of small-diameter aluminum wire joined to ceramic substrates metalized with thin-film and thick-film gold. Quick testing technique for nondestructive location of poor wire bonds is also presented.